1. Technical Field of the Invention
The present invention relates generally to an optical distance measuring apparatus designed to transmit a laser beam in a cycle and to receive a return of the laser beam from an object to determine the distance to the object, and more particularly to such a distance measuring apparatus having a matrix of light sensitive cells which are selectively activated in each scan cycle for minimizing optical interference with incoming light other than a return of a laser beam in determining data on the distance to an object.
2. Background Art
Automotive distance measuring systems are known in the art which are designed to transmit laser beams intermittently over an angular range embracing an automobile and receive a return of the laser beam to determine the amount of time required by the laser beam to travel to and return from a reflective object. It is advisable for such distance measuring systems to broaden an area scanned by laser beams in order to increase a detectable range.
The broadening of the scan area, however, requires increase in light sensitive area covered by light sensitive cells installed in a receiver, which may cause a laser beam outputted from a distance measuring system installed in an oncoming vehicle or another vehicle traveling on an adjacent lane to be received undesirably, thus resulting in errors in measuring the distance to a target object.
In order to avoid the above problem, Japanese Patent First Publication No. 7-98381 teaches a radar system which has an array of light sensitive cells in a receiver and activates some of the light sensitive cells selected as a function of a direction of emission of a laser beam, thereby decreasing an area receiving a return of the laser beam to minimize unwanted optical disturbances.
The determination of two-dimensional position of a target object, however, requires changing the direction of emission of laser beams two-dimensionally as well as arraying light sensitive cells in a matrix arrangement. The former requires a horizontal scan mechanism for scanning a laser beam in a width-wise direction of the vehicle and a vertical scan mechanism for scanning a laser beam in a height-wise direction of the vehicle, thus resulting in complexity of a structure of the radar system. For example, a scan system designed to emit laser beams over a given angular range through reflections on a mirror requires a mechanism for turning the mirror in two directions: vertical and horizontal directions, which also results in complexity of control for the movement of the mirror.